Field of the Invention
The present invention relates to a method for machining a workpiece and to a machine tool.
Discussion of the Background
Concerning forming of a groove portion on a surface of a workpiece, for example, machining of a groove portion that constitutes a tooth surface of a gear wheel, a technology is known in which a milling tool (gear milling cutter) including a plurality of cutting edges at regular intervals on an outer periphery surface of the milling tool is used. In the technology, after the milling tool is rotated and the cutting edges have been moved to a depth of cut of the workpiece, machining is performed by feeding the milling tool and the workpiece relatively (see Japanese Patent Application Laid-Open Publication No. 2012-66380: patent document 1).
The gear milling cutter described in the patent document 1 includes a plurality of root inserts and a plurality of flank inserts on both sides of the cutter. The root inserts are disposed at regular intervals adjacent to the outer periphery surface of the disc-shaped basic body. Furthermore, the flank inserts are disposed inward from the root inserts in a radial direction of the basic body at regular intervals.
In this case, making the disposition of the root inserts and the flank inserts approximately equal to the shape of the actual tooth surface to be machined achieves high precision machining as long as rigidity of the cutter is ensured, because the root inserts perform machining of a bottom face and a deep area of lateral faces of the tooth surface and the flank inserts perform machining of the shallow area of the lateral faces of the tooth surface, simultaneously.
However, concerning the gear milling cutter described in the patent document 1, in a case that a specification such as the number of the tooth and a pitch or a module of the gear wheel to be produced is different, a different cutter on which the inserts are disposed so that they meet the specification is required for each machining.
In particular, many inserts of at least two types that differ in their shapes (root insert and flank insert) need to be disposed on the cutter in order to constitute a gear milling cutter of one specification, therefore it takes time to mount each insert accurately. Moreover, because poor managing of wear condition of each insert may cause defects in machining, frequent checking of the inserts is needed. The above two factors lead to higher costs.
Furthermore, in this configuration, a depth of cut to be machined at a time on a workpiece should be at least a depth up to the root insert. This makes counter force that the gear milling cutter receives higher, therefore the power to feed the cutter needs to be inevitably higher.
As a way of solving these problems, another method is known in which machining of the tooth surface of the gear wheel is performed with a disc-shaped milling tool (side cutter) on which a plurality of cutting inserts are disposed at regular intervals on the outer periphery surface of its disc-shaped basic body. Each of the cutting inserts includes a cutting part both on the outer periphery surface side and on the lateral face side of the basic body. (see Japanese Unexamined Patent Application Publication No. 2013-543450: patent document 2).
The method of machining a gear wheel described in the patent document 2 includes feeding the above-mentioned side cutter and the workpiece relatively in the direction perpendicular to an axis of rotation of the side cutter. This achieves machining by one moving to a depth of cut.
Moreover, various curved surfaces can be machined by swiveling the axis of rotation within a plane perpendicular to the direction of the length of the tooth surface.